This application claims the benefit of foreign priority under 35 U.S.C. .sctn. 119 of Japanese Application No. 10-104810 filed on Apr. 15, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an on-off control circuit of a work lamp mounted on a motor vehicle in which the work lamp serves to illuminate the cargo bed, etc. of the vehicle. More particularly, it relates to an improvement of the circuit for controlling a work lamp mounted on a vehicle, the work lamp comprising a white lamp for illuminating the rear of the vehicle.
2. Description of Related Art
Work lamps for illuminating the cargo bed, etc. of a truck so that work such as loading and unloading of goods can be carried out at night are known. A work lamp of this sort is switched on and off by the driver or other operator. However, if the driver forgets to turn off the work lamp after the work is finished and drives off in the vehicle with the lamp still lit, the drivers may incur problems. For example, traffic regulations in many countries stipulate that a vehicle shall not be driven while a work lamp is lit. Furthermore, because work lamps usually take electric current from the battery carried by the vehicle, having a work lamp unnecessarily and wastefully lit drains the battery.
The present applicant has previously filed Japanese Patent Application No. 8-283653 (hereinafter referred to as the '653 application), which relates to a work lamp on-off control circuit directed to obviating the shortcomings of the prior art. The '653 application disclosed a circuit for ensuring that a work lamp does not remain carelessly lit while the vehicle is travelling and only lights up when the parking brake is operative. According to this circuit, once the parking brake has been released, an action which would otherwise turn the work lamp on is overridden and the work lamp is actively turned off.
Motor vehicles fitted with an implementation of the invention disclosed in the '653 application have been sold. However, drivers operating vehicles in places where the land is extremely flat, such as in North America, have the habit of not always operating the parking brake when they stop their vehicle. There is therefore a need for an improvement of the conditions under which a work lamp can be turned on.